Attachment Structure for Brush Holder Springs

The present invention relates to an attachment structure for brush holder springs in a DC motor employed as a drive source in an automotive windshield wiper, power window regulator, or the like.

One conventional attachment structure for a motor brush holder spring includes a brush holder molded integrally of synthetic resin. Brushes are supported on brush holder springs to which terminals are spot-welded for connection to leads. The assembly of the brush holder springs, the brushes, and the terminals is attached to the brush holder by insert molding. However, the brush holder springs tend to be reduced in resilient forces produced thereby because of the molded nature of the brush holder and the heat generated when the brush holder is molded at a temperature in the range of from 200.degree. to 240 .degree.C.

It is an object of the present invention to provide an attachment structure for brush holder springs, which permits the brush holder springs to be easily attached to a motor bracket, keeps the brush holder springs firmly anchored to the motor bracket, and allows the attached brush holder springs to press brushes mounted thereon against a commutator under sufficient resilient forces.

According to the present invention, an attachment structure for brush holder springs in a motor includes a motor bracket to be mounted on a motor frame and having a pair of diametrically opposite projections on inner peripheral wall surfaces thereof, and a pair of brush holder springs supporting on one end portion thereof brushes for sliding contact with a motor commutator and having on opposite end portions thereof gripping members fitted complementarily over the projections, under resilient forces. Since the brush holder springs are attached to the motor bracket under resilient forces, the brush holder springs can be anchored in position to the motor bracket. The attachment structure is composed of a reduced number of components, can be manufactured easily, and can be assembled efficiently.

The present invention will be described in detail by way of illustrative example with reference to the accompanying drawings, in which;

FIG. 1 is a fragmentary longitudinal cross-sectional view of a DC motor incorporating a conventional attachment structure for a brush holder spring;

FIG. 2 is a cross-sectional view taken along line II--II of FIG. 1;

FIG. 3 is a perspective view of a brush holder in the attachment structure shown in FIG. 1;

FIG. 4 is a fragmentary longitudinal cross-sectional view of a DC motor incorporating an attachment structure for a brush holder spring according to the present invention;

FIG. 5 is a cross-sectional view taken along line V--V of FIG. 4; and

FIG. 6 is a perspective view of a brush holder in the attachment structure illustrated in FIG. 4.

FIGS. 1 through 3 shows a conventional attachment structure for attaching a brush holder spring in a DC motor. Carbon brushes 1 are supported on a pair of brush holder springs 2, respectively, attached at ends thereof to a brush holder 4 integrally molded of synthetic resin. Terminals 3 for connection to leads (not shown) are spotwelded to the springs 2 near the attached ends thereof. The brush holder 4 is fastened by a screw 6 to a motor bracket 5 mounted on an axial end of a motor frame 7 accommodating therein magnets 8 secured to inner wall surfaces thereof. The motor bracket 5 is normally made of aluminum by die casting. A rotor 9 is mounted on a shaft 10 rotatably supported by the motor bracket 5. A commutator 11 is also mounted on the shaft 10 and held in sliding contact with the brushes 1.

The assembly of the brushes 1, the brush holder springs 2, and the terminals 3 is attached to the brush holder 4 by insert molding. The brush holder springs 2 tend to be reduced in resilient forces produced thereby because of the molded nature of the brush holder 4 and the heat generated when the brush holder 4 is molded at a temperature in the range of from 200.degree. to 240.degree. C.

FIGS. 4 through 6 illustrate an attachment structure for a brush holder spring according to the present invention. Those parts shown in FIGS. 4 through 6 which are identical to those of FIGS. 1 through 3 are denoted by identical reference numerals employed in FIGS. 1 through 3, and will not be described in detail.

A motor bracket 12 molded of synthetic resin is attached to the axial end of the motor frame 7. The motor bracket 12 has a pair of diametrically opposite steps 14 defined on inner peripheral side wall surfaces thereof, and a pair of diametrically opposite projections 15 projecting axially and radially inwardly on the steps 14. Each of the projections 15 has a transversely cross-sectional shape resembling that of a dovetail, such that its radially inward end is wider than the radially outward end thereof. A pair of brush holder springs 13 supporting the carbon brushes 1 on one end portion thereof is securely mounted in the motor bracket 12. More specifically, each of the brush holder springs 13 has a straight portion 13a supporting the brush 1 thereon and an arcuate portion 13b held against an arcuate inner wall surface of one of the steps 14 of the motor bracket 12. The arcuate portion 13b includes an integral dovetail-shaped gripping member 16 fitted complementarily over one of the projections 15. When attaching each brush holder spring 13, the gripping member 16 is force-fitted over the projection 15 in the axial direction of the motor bracket 12. The attached brush holder spring 13 is prevented from being displaced radially because of the dovetail joint between the projection 15 and the gripping member 16. The step 14 serves to position the brush holder spring 13 in the axial direction with respect to the motor bracket 12 and hence to position the carbon brushes 1 in the axial direction with respect to the commutator 11.

The gripping member 16 is contoured complementarily to the shape of the projection 15 by bending the arcuate portion 13b of the brush holder spring 13. The gripping member 16 is firmly attached to the projection 15 under its own resiliency, as well as due to the dovetail joint.

The straight portion 13a of each brush holder spring 13 has a dovetail-shaped gripping member 17 similar to the gripping member 16. The carbon brush 1 is securely anchored to the straight portion 13a by the gripping member 17. The gripping member 17 has a pointed tooth 18 projecting into biting engagement with the carbon brush 1 retained by the gripping member 17 for preventing the carbon brush 1 from moving in the axial direction of the shaft 10.

Although a certain preferred embodiment of the present invention has been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.